1. Field of the Invention
The present invention relates to zip fasteners and more particularly, to a method for making a waterproof, airtight, anti-slit, high transverse tensile strength double-layer zipper and a waterproof, airtight, anti-slit, high transverse tensile strength double-layer zipper thus made.
2. Description of the Related Art
Most conventional polyester zippers are of a single layer design 7 (see FIG. 1). After stitched an interlocking series of teeth to each of two zipper tapes, a waterproof film (not shown) is coated on or bonded to the back walls of the two zipper tapes, and then use a thin cutter blade to cut off the waterproof film between the two zipper tapes, and then attach a zipper slider to the two interlocking series of teeth. This single layer design polyester zipper can provide a simple waterproof function when receives no transverse force, however, it is not airtight. The claims and embodiment in U.S. Pat. No. 4,601,085 discloses a double-layer zipper 8 (see FIG. 17) for diving suit. This design of double-layer zipper effectively achieves waterproof and airtight effects. In order to achieve the expected waterproof function, the intermediate fabric tape 82 has a certain thickness and the tape edge 821 protrudes over the end edges 81 of the upper and lower interlocking series of teeth 8 at a distance 80, however, these features tighten the sliding movement of the zipper slider to close the zipper, causing friction between the interlocking teeth and the zipper slider and shortening the lifespan of the zipper.
Further, according to the aforesaid prior art design of U.S. Pat. No. 4,601,085, in addition to the drawback that the tape edge 821 protrudes over the end edges 81 of the upper and lower interlocking series of teeth 8 at a distance 80, the large thickness of the coating of flexible glue 9 makes the structure of the intermediate fabric tape 82 and the coating of flexible glue 9 not steady, affecting the sliding smoothness of the zipper slider (not shown), and the interlocking teeth may be forced out of engagement position when the zipper slider is pulled with force. If a hard glue coating is used to substitute for the coating of flexible glue, the zipper slider may become immovable. Therefore, this prior art design of double-layer zipper can simply be used in diving suits, not applicable to other waterproof articles.